268 



The National Geographic Magazine 



products of rock disintegration are car- 

 ried by moving ice and deposited there- 

 from, they are called glacial drift. When 

 they are carried by wind, as is often the 

 case, they are called seolian soils. The 

 above are some of the varieties of soils 

 as determined by their method of for- 

 mation. Soils are also classified in re- 

 gard to their chemical characters ; as, 

 for instance, when formed from the 

 decay of carbonate of lime, they are 

 called limestone soils. When arising 

 from the disintegration of granite, they 

 are called granitic soils. When formed 

 chiefly from particles of silex, they are 

 called sandy soils. When consisting 

 mostly of silicate of alumina, they are 

 called clay soils, and so on. 



But for agricultural purposes the soil 

 consists of more than decayed mineral 

 matter. By the decay of organic mat- 

 ter there is introduced into the soil the 

 element, humus, which is one of its 

 principal characteristics from an agri- 

 cultural point of view. The soil is 

 filled with millions of organisms of a 

 lower form, without whose activity the 

 growing of crops would be impossible. 

 The soil, therefore, not only contains 

 the mineral matters which are neces- 

 sary to sustain the life of plants, but 

 also those organic elements without 

 which these mineral matters would not 

 be available for plant growth. The 

 three principal mineral foods of plants 

 are potash, phosphoric acid, and nitro- 

 gen. Lime, magnesia, iron, and many 

 other mineral substances are also found 

 in plants, but these are not absolutely 

 essential to plant growth. If, however, 

 either nitrogen, potash, or phosphoric 

 acid be entirely removed from the en- 

 vironment, it is impossible to produce a 

 matured plant. The great bulk of the 

 material of which plants are composed 

 is not drawn, however, from the soil, 

 but is taken from the air and water. 

 Great as have been the chemical achieve- 

 ments of man, no chemist has yet arisen 

 whose skill can be compared to that of 



the plant itself. Any chemist who 

 to-day, with all the appliances which 

 science has placed at his disposal, could 

 make by synthesis the various organic 

 compounds of which plants are princi- 

 pally composed would rival the fame of 

 Berzelius, Liebig, Hoffman, Berthelot, 

 Gibbs, or Remsen. Thus the soil must 

 be regarded as that part of plant life 

 which furnishes the chemical support 

 for the growing plant, supplies it with 

 the mineral foods essential to its growth 

 and maturity, and favors best those 

 conditions which enable the plant cell 

 to elaborate the organic matters of 

 which the matured plant is chiefly 

 composed. 



THE UNITED STATES AN AGRICUL- 

 TURAL COMMUNITY 



Having thus briefly described how the 

 soil originated, we pass to the considera- 

 tion of the second part of the subject, 

 namely, the crops which grow therein. 



The United States is essentially an 

 agricultural community. The basis of 

 its wealth lies not so much in the pro- 

 ducts of its mines and manufactures as 

 it does in those of its fields, gardens, 

 orchards, and forests. The territory of 

 the United States, including its new pos- 

 sessions, represents every variety of soil 

 and every character of climate. It has 

 agricultural lands in the tropics, in the 

 subtropics, in the temperate zone, and in 

 the sub-boreal regions of Alaska. In 

 latitude its agricultural lands extend 

 half way around the world. Agricult- 

 ural crops are grown in the United States 

 subject to all the vicissitudes of climate, 

 to excessive rainfalls, to prolonged 

 drouth, to intense heat, and to alternat- 

 ing frosts and sunshine. 



Within the borders of the United 

 States are grown every agricultural crop 

 known to the world. It produces im- 

 mense quantities of the cereals; of fiber 

 plants, including especially cotton and 

 flax; of sugar-producing plants, includ- 

 ing sugar cane, sugar beets, sorghum, 



